Electromagnetic brake assemblies are old and well known in the art. A primary use for such brake assemblies is to brake electric motors, such as those used on hoists and cranes. Illustrative of art known to applicant is U.S. Pat. Nos. 2,462,017, 2,506,028, 2,543,830, 2,668,920, 2,727,163, 2,983,339, 3,171,515, 3,224,540, 3,335,304, 3,357,528, 3,554,335, 3,555,317, 3,659,170, 3,665,231, 3,741,353, 3,763,968, 3,784,852, 3,826,342 and 3,944,028.
An electromagnetic brake assembly is generally contained in a housing fastened to the end of a gear box or electric motor. A brake wheel in the housing is fixed to a drive shaft or the gear box or electric motor, with a pressure plate assembly having at least one brake liner spaced axially from it. The pressure plate assembly is non-rotatably mounted in the housing to move axially on actuation and permit the brake liner to engage the brake wheel to slow and stop the rotation of the motor shaft. The pressure plate is typically urged against the brake wheel by a mechanical bias when the brake assembly is not operating.
The axially movement of the pressure plate assembly is controlled by an electromagnet or electromagnets mounted axially of the pressure plate. To operate the motor, the brake is released by electrically activating the electromagnet, which draws the pressure plate assembly axially away from the brake wheel against the force of the mechanical bias to permit the drive shaft to rotate. The pressure plate assembly is held away from the brake wheel during operation of the electric motor by continual operation of the electromagnet or by secondary means that maintains the pressure plate assembly at a released position. When the motor is stopped, the brake stops the rotation of the motor shaft by allowing the pressure plate assembly to move axially under the force of the mechanical bias to bring the brake liner into engagement with the brake wheel.
One of the primary problems with such electromagnetic brake assemblies is lack of adjustability of the axial distance or gap between the brake wheel and the brake liner of the pressure plate assembly. The air distance varies with the tolerance of the brake assembly and the wear of the brake liner. The mechanical bias urging the pressure plate assembly against the brake wheel is generally an adjustable spring, but adjustment of the spring only compensates for variations in the gap by increasing the force exerted on the pressure plate. By such compensating adjustment increased wear on the brake liner also results, decreasing the useful life of the brake liner.
Another problem with such electromagnetic brake assemblies is lack of cooling of the brake liner during operation of the brake. Wear of the brake is hastened because of lack of dissipation of the heat from the brake liner during operation. In fact, the electromagnetic brake assembly usually has no cooling means to dissipate the heat generated during operation of the brake.
The present invention overcomes these difficulties and disadvantages of prior electromagnetic brake assemblies. It provides means for adjusting the distance between the brake wheel and pressure plate assembly without increasing the force exerted on the pressure plate or varying the force exerted by the electromagnet. Further, it provides a means for cooling the brake liner during operation of the brake assembly, preferably by the power of the drive shaft to be braked by the assembly.